How to create the dead message queue

Just to understand your question correctly:
You have an MQTT QoS consumer, that consumes messages from a dynamically created queue. And the question is: How to create a Dead-Message-Queue (DMQ) for that scenario ?

1. define a DMQ (name it as you like) (as an example: We use DMQ1 as name here)
2. create a template queue with all parameters for the dynamically created MQTT-client-queue. One of that parameters it : Set the DMQ to the queue defined in step 1. (Just for explanation: defining a template queue is identical to defining a "normal" queue) (as an example, we use mqtt-client.template_q as name here)
3. In the client-profile for the MQTT-client (this can even be the default-profile) define a "copy-from-template"-queue with the name of the queue created in step 2.

If you have done all that, these things will happen when the MQTT client connects:

• client-profile says: "Use mqtt-client.template_q as template for client-dynamic queue"
• After creating the dynamic queue, there is a defined parameter "DMQ = DMQ1"
• And all messages discarded to DMQ will be stored in DMQ1.

Does that help you ? Do you need details for each step ?

Yes, the DMQ is just a regular queue.